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Thread: Rod bearing replacement

  1. #1
    Join Date
    Apr 2019
    Posts
    7

    Rod bearing replacement

    Hey guys,
    I picked up my 2007 SX4 AWD a few months ago. It has around 160k miles on it. On Tuesday just before I left on a business trip, it started knocking. As soon as I heard it, I pulled into the closest parking lot and shut it down. I checked the oil and it wasn't showing on the dip stick. The weird thing is that it was changed right before I bought it and I've checked it every couple of weeks and the level was fine. I can't find a major leak anywhere and it doesn't seem to be burning oil either.

    Anyway, my main question is about changing the rod bearings. I don't have money to buy a used (much less rebuilt) engine. I drained some oil out this morning and there are no chunks or even large enough particles of anything that can be seen. Only a metallic sheen in the oil. Do you think that this is evidence that I can do the rod bearing swap with the motor in the car? I've done several engine rebuilds, so I know the basics. If I had the time and money, I'd rebuild the motor, but at this time of life, it's not really possible.

    If any of you have done rod bearing swaps in the car, do you have any tips? And what were your results? Did they last a decent amount of time?

    Thank you for the help!!
    Chad

  2. #2
    Join Date
    Nov 2010
    Location
    Las Vegas, NV
    Posts
    2,093
    Hey there,

    I purchased an SX4 from a member that had the same situation as you and someone else and I worked on fixing it. We were going to swap engines but he found that it was just a spun rod bearing. Like you, the former owner shut it down in time to prevent serious damage. We replaced the rod bearing from underneath with little problem. The car had some other issues that sprung up afterwards and we ended up giving it away to someone who needed it, but at the time we had it, the bearing seemed to hold and I never had that friend tell me there was a knocking when he drove it occasionally after we gave it to him.
    The path to heaven runs through miles of clouded hell.

  3. #3
    Join Date
    Apr 2019
    Posts
    7
    Quote Originally Posted by Brumbie13 View Post
    Hey there,

    I purchased an SX4 from a member that had the same situation as you and someone else and I worked on fixing it. We were going to swap engines but he found that it was just a spun rod bearing. Like you, the former owner shut it down in time to prevent serious damage. We replaced the rod bearing from underneath with little problem. The car had some other issues that sprung up afterwards and we ended up giving it away to someone who needed it, but at the time we had it, the bearing seemed to hold and I never had that friend tell me there was a knocking when he drove it occasionally after we gave it to him.
    Thank you for that feedback, it's very helpful and encouraging!
    I plan to pull it apart before buying any parts because I've read that there are possibly 3 different size OE bearings that could have been used.

    Did you replace only the one spun rod bearing, or did you replace all of them?

    Thank you,
    Chad

  4. #4
    Join Date
    Oct 2017
    Posts
    191
    Just slapping in new bearings after such an incident is a high risk procedure. Every now and then, you can find one where the crankshaft journal and connecting rod didn't get messed up, but that is rare. A periodic lack of lubrication can cause a bearing to slowly wear down until there's a whole bunch of slop in there and the crankshaft journal can beat away at the bearing and even loosen it from the rod and not damage anything but the bearing. But a lot of planets need to align for that to happen.

    If the bearing actually SPUN inside the rod due to it seizing to the crankshaft, which is the usual cause of a knocking connecting rod, the chances of long-term success is zero. The bearing can no longer be clamped inside of the big end of the connecting rod and that is pretty critical in order for the oiling hole in the bearing to stay lined up. In addition, the bearing needs a smooth surface to run on, and it is always galled up when a bearing welds itself to a crankshaft.

    As far as the different sized bearings that could have been used from the factory, I wouldn't worry about that. The difference in size from one bearing to another would be within .0005". Any engine with any appreciable mileage to it is going to have variations beyond that. It may be worth the time and effort to go through that in order to sell a smooth running car on the showroom floor, but not for a back yard fix-up engine.

    Unless you REALLY know what you are doing, I am going to say that it isn't worth the time and effort to try throwing new rod bearings at it.

  5. #5
    Join Date
    Apr 2019
    Posts
    7
    Thank you for your input and insights. I do believe that I caught it and shut it down in time that it will be salvageable, however, there's no way to know until I get in there.
    The fact that this can be risky and is not the BEST option is very true and I understand that. I'm looking for tips and advice to make it as successful as possible. The other fact is that I don't really have another option at this point. We don't have the money to buy a used or rebuilt motor. I don't have the time for a full, proper rebuild, and I definitely don't have the money to pay someone else to do it. So I'm kinda stuck anyway. I appreciate the help, and I'll post a report of how it goes.
    Thank you,
    Chad

  6. #6
    Join Date
    Apr 2019
    Posts
    7
    Another quick question,
    What is the torque spec for the rod bolts and for the oil pan bolts?
    Thank you,
    Chad

  7. #7
    Join Date
    Oct 2017
    Posts
    191
    Well, once the bearing welds itself to the crankshaft, the damage is done. I do not know how to think more positively about the matter. It tears things to shreds and the big end of the connecting rod is probably no longer perfectly round like it needs to be. The damage is done at the moment you hear the noise. But shutting it off early, that only increased the chances of not having metal particles get spread around all the oil passages and into the timing chain tensioner, etc.

    If it was a knock that gradually got worse and worse, you may have a chance. If it happened suddenly, lets just say that it'll be a hands-on learning project at best.

    Torque specifications for connecting rod bolts according to Mitchell is 11 ft lbs followed by 45 degrees turn of each bolt and then another 45 degree turn of each bolt.

    Oil pan bolt torque... forget that. Tight enough to not come loose and loose enough that you don't break the bolt.

    "Engine crankcase bolts with 8mm threads" is 19 ft lbs.
    "Engine crankcase bolts with 10mm threads" is 42 ft lbs.

    That is all I can find on oil pan bolts.

  8. #8
    Join Date
    Oct 2017
    Posts
    191
    P.S. I would be really happy if you can prove me wrong and save the engine.

  9. #9
    Join Date
    Feb 2013
    Posts
    1,137
    Its safer, easier and cheaper to swap the engine.

  10. #10
    Join Date
    Apr 2019
    Posts
    7
    Last night I was able to finish tear down and get the oil pan removed. Here's a pic of what I found in the pan. There is obviously bearing material there. The big black chunks are gasket material from the inside of the pan where it mates to the bottom of the block.



    I think I found what could be the best case senario for this bad situation. Connecting rods #1, 2, & 3 were tight on the crank journal with only a slight amount of axial play but no detectable radial play. Number 4 had a very noticeable amount of radial slop. I pulled the cap and was happy to see that although the bearing was toast, it was still fully encircling the journal.



    The crank journal doesn't look too bad. It is scuffed up good, but no gouges big enough for my finger nail to catch on or feel. I'm hoping I can polish it nice enough make this work.



    I'm planning to get the bearings and everything else I need in time to get it all back together on Saturday.
    Question, since I am trying to save as much money as possible by going this route, do I NEED an oil pan gasket? Or can I just use silicone?

    Stay tuned...

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